ASGSB 1999 Annual Meeting Abstracts

CORTICAL MICROTUBULES FORM A DYNAMIC MECHANISM WHICH HELPS REGULATE THE DIRECTION OF PLANT GROWTH. C.W. Lloyd¹, R. Himmelspach², C.L.Wymer 1 and P. Nick². ¹ Dept of Cell Biology, John Innes Centre, NORWICH NR4 7UH, UK, and ²Institut fur Biologie II, Schanzlestr.1., 79104, Freiburg, Germany.

This paper will review the effects of various factors, including gravity, on microtubule (MT) reorientation, together with other biochemical work on microtubule-associated proteins (MAPs) which regulate MT behaviour.

Cortical MTs tend to form transverse “hoops” around elongating cells, acting as a template for the deposition of corresponding patterns of cellulose which maintain axial growth. Factors such as unilateral light, plant growth regulators and gravity can cause the MTs to reorientate and the direction of cell expansion to change. In a recent study, we gravitropically-stimulated dark-grown maize seedlings by placing them horizontally on glass slides. Epidermal cells on the upper flank elongated more than the cells on the lower flank, giving rise to the bending by which the coleoptile restored the vertical axis. Immunofluorescence of fixed tissue showed that cells on the lower flank tended to have transverse MTs (consistent with elongation) whereas cells on the upper flank underwent reorientation to longitudinal (consistent with an inhibition of elongation). To investigate this gravity-induced reorientation in living cells we microinjected fluorescent tubulin into cells on the upper flank. This showed that the MT array went through a ‘mixed’ phase as one array of essentially parallel MTs was replaced by an array in a new direction - a pattern previously seen with hormone-induced reorientation.

The Norwich lab’ has also isolated proteins which influence the properties of MTs in vitro and these are likely to be involved in regulating the organization of the MT array in cells.

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